1. Technical Field
The present invention relates to a boss for a composite pressure container. The invention especially relates to a boss especially adapted to withstand pressure for the whole duration of the life cycle of the composite pressure container.
2. Description of the Related Art
This invention concerns an improved boss for a composite pressure container for fluids. The container includes an inner fluid-tight thermoplastic liner layer and a pressure supporting layer formed by winding fibre-reinforcement onto the liner layer, as well as at least one central aperture in at least one end, for provision of a boss for mounting a coupling or a valve member.
A boss for composite pressure containers is disclosed in Norwegian Patent No. 312048. Composite pressure containers are disclosed in Norwegian Patents No. 306226 and 309667.
Pressure containers like these are subject to numerous and varied types of stress and forces. Mainly, this regards the inner over pressure which may occur when filling the container with fluids. The inner pressure will influence the boss with an axially outward directed force which may be considerable. Additionally, the boss construction may be influenced by an axially inward directed force, e.g., when a valve or coupling member is mounted to the boss, and possibly by unintended stress caused by impacts or blows. It is important that the construction and mounting/fixation of the boss is also capable of resisting such forces. The same is valid for torsion forces which may occur when, for instance, the valve member is mounted onto the boss, which is usually formed with threads and screwed into the boss. Torsion forces to be concerned in this regard could also occur when the fibre reinforcement is winded onto the inner liner. It is especially important that the boss provides a safe and durable seal against the adjacent parts of the pressure container. The sealing has to be such that the above-mentioned forces are not damaging to the sealing effect.
Norwegian Patent No. 312048, mentioned above, discloses a boss suitable for use in the present type of pressure containers.
Composite pressure containers can contain different fluids such as propane and butane, for domestic use often with a relatively low maximum pressure of about 35 bars. The containers can also hold fluids such as CNG, hydrogen and other industrial gas types often requiring a higher maximum pressure of about 200 bars. Composite pressure containers may be adapted to withstand test pressures up to 2000 bars or even higher.
The prior art disclose the use of O-rings to seal the passage between a boss and a coupling or valve member. When the container contains a fluid, the O-ring will be in contact with the fluid present in the container. The present inventors have observed that the O-rings under the prevailing conditions within a boss have a tendency to swell when in contact with the fluid. The swelling of and pressure from the O-rings may cause indentations in the opposing sealing surfaces which subsequently may cause leakage for instance if the coupling or valve member or the O-rings are changed.